I/O priorities

The database server prioritizes disk I/O by assigning different types of I/O to different classes of virtual processors and by assigning priorities to the nonlogging I/O queues.

Prioritizing ensures that a high-priority log I/O, for example, is never queued behind a write to a temporary file, which has a low priority. The database server prioritizes the different types of disk I/O that it performs, as the table shows.
Table 1. How database server prioritizes disk I/O
Priority Type of I/O VP class
1st Logical-log I/O CPU or LIO
2nd Physical-log I/O CPU or PIO
3rd Database I/O CPU or AIO
3rd Page-cleaning I/O CPU or AIO
3rd Read-ahead I/O CPU or AIO

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